If straight vinegar won't work, Windex probably won't either. The ammonia-free Windex has a vinegar (approximately 3% acetic acid) base anyway.
The deposits may be pretty well etched into the glass if straight vinegar won't remove them. You could try a long, 12to 24 hour straight vinegar soak, as it might take some time for it to react with the calcium deposits enough to remove them. Although I don't think whatever you attempt to clean the glass with (as long as frogs aren't present, of course) is going to hurt anything as long as you end it with plenty of rinsing in clear water to remove any trace of residue, and a long airing out--72 hours or so, you can't always be absolutely sure. It's not just the glass, but the silicon sealant that may absorb some of the stuff you use and is less easily rinsed away.
I've actually soaked old tanks in 2% chlorox solution overnight, rinsed, and soaked again with straight white vinegar for 14 hours, scrubbed and rinsed and then let them air outdoors in the sun for 72 hours with no problems. Diluted chlorox dissipates and breaks down with time, and is no longer present at all after a vinegar soak. Vinegar isn't toxic, and there are no fumes to annoy once it has been rinsed and aired out. Of course, you have to buy a heck of a lot of white vinegar to fill a tank. It used to be 19 cents a gallon, but is not longer that cheap.
On the other hand, if you're spending what the darts cost, it seems that what was suggested about purchasing a new tank is rational. There's an old saying among horticulturists that it is better to plant a $5.00 tree in a $30.00 hole than the reverse.
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Patty
Pahsimeroi, Idaho
4 D. auratus blue
5 D. galactonotus pumpkin orange splash back
5 D. imitator
6 D. leucomelas
4 D. pumilio Bastimentos
4 D. fantasticus
4 P. terribilis
4 D. reticulatus
4 D. castaneoticus